We continued to study the most repetitious family of gene sequences in mammalian genomes, the Alu-related short interspersed elements. Although the exact function of these mobile elements remains unknown, they are known to cause human heritable disorders by RNA and DNA mediated mechanisms. Their expression into RNA was studied in growth and development. Their metabolism was studied at the levels of transcription, post-transcriptional processing and cytoplasmic accumulation. The RNAs were characterized in terms of primary and secondary structure, copy number, subcellular localization, and interaction with components of the protein synthetic machinery. A. Studies of the regulation of small cytoplasmic (sc) B1-AluRNAs 1. Tight regulation of scB1-Alu RNA was detected among fetal and adult tissues. In addition, the effects of growth and transformation on B1-Alu RNA levels were studied. 2. The effects of cis-acting elements of a scB1-Alu RNA gene on transcriptional initiation and post-transcriptional processing was studied in-vitro and in-vivo. Additional analyses revealed novel regulation at the level of transcriptional termination in-vitro and in-vivo. 3. A B1-Alu RNA post-transcriptional processing enzyme was identified in nuclear extracts of amphibian, mouse and human cells and partially characterized. B. Characterization of scB1-Alu RNA; structural analyses and interaction with cellular components. 1. cDNAs of scB1-Alu RNA were cloned and characterized in terms of primary and secondary structure; this revealed a novel subset of evolutionarily conserved RNA structures. 2. scB1-Alu RNA was localized to the slow velocity- sedimentation fraction of the cytosol and was determined to be ~1000 fold less abundant than the small structural RNAs 7SL and 5S. 3. Specific binding of scB1-Alu RNA to polyribosome-associated proteins was demonstrated. 4. The scB1-Alu RNA-associated Be protein (Ro; human autoantigen) was studied.